German Published Patent Application No. 31 18 425 (corresponding to U.S. Pat. No. 4,426,981) describes a method and a device for controlling an internal combustion engine, in the case of which the fuel quantity injected into the combustion chambers of the internal combustion engine and the supply onset (start of pump delivery) or the onset of injection is detected by means of a pressure sensor. If the differentiated output signal exceeds a threshold value, the onset of injection is recognized. In the case of zero passage for the twice differentiated pressure signal, end of injection is recognized. A fuel-quantity signal results on the basis of the difference between the onset of injection and the end of injection.
An arrangement for detecting the beginning of injection in the case of a diesel internal-combustion engine is likewise known from German Published Patent Application No. 36 12 808 (corresponding to U.S. Pat. No. 5,107,700). It describes detecting the beginning of injection when the output signal from a pressure sensor exceeds a threshold value. The threshold value is formed in dependence upon the peak value of the pressure signal from the preceding injections.
A disadvantage of these methods and devices is that the interference pulses in the pressure signal are recognized as injection-onset or as end-of-injection signals. This, in turn, leads to faulty fuel metering or, in devices where the fuel-quantity signal is used as an injection-duration signal for additional control devices, leads to faulty controlling of the additional devices, such as, for example, of the exhaust-gas recirculation rate.
An object of the present invention, in the case of a method and a device for controlling an internal combustion engine, is to distinguish interference pulses from the useful signal.